\chapter{Introduction}

Optical mesh networks have underwent a rigorouls evolution cycle. With the introduction of optical (D)WDM transport, 
they have begun to replace older SONET/SDH ring-based models due to being able to maintaining 
fast recovery times in case of failure while also providing a more robust capacity efficiency 
model and cheaper deployment and upgrade scenarios (TODO ref ken liu IP/WDM). The latest emerging technologies in such 
networks aim to eliminate the costly process of opto-electronic conversions by 
introducing Reconfigurable Optical Add-Drop Multiplexer (ROADM) systems.
%Optical networks that incorporate ROADM systems are said to be transparent because of their capability to switch signals on the wavelength level without the need for OEO conversions. 
In addition, ROADMs provide the capability of dynamic reconfiguration of end-to-end lightpaths making optical mesh networks a highly scalable and dynamic environment.

\section{DAS-4 Photonic Cross-Connect network}

The Distributed ASCI Supercomputer 4 (DAS-4) is a computational grid comprised of wide-area, geographically-disjoint clusters used for computer and science research in the Netherlands. DAS-4 consists of eight clusters (TODO: correct num of clusters?) located in the campus facilities of four Universities - UvA and VU in Amsterdam, Leiden University and TU Delft - with one located in the Netherlands Institute for Radio Astronomy (ASTRON). The primary usages of the DAS-4 testbed are Grid-based applications and distributed systems whose data sets target research data collected from disciplines such as Computer Science, Radio Astronomy and genome sequencing in Biological studies. 

DAS-4's clusters are connected together via a transparent all-optical network which uses SURFnet's 
(a Dutch National Research and Education Network) DWDM infrastructure. A Degree-4 Fast Photonic Cross-Connect (FPX) (TODO ref) provides Layer 0 wavelength (Fig x a)services for dynamic link establishment and capacity provisioning. Therefore, routed and routing network traffic is transported  between Layer 3 nodes at each cluster without leaving the optical layer. By incorporating particular wavelength selective switches (WSS) (Fig x b), the FPX supports dynamic reconfiguration in addition to remote management. Those capabilities enable DAS-4's network to cope with multi-cluster workloads on-demand and fulfill the requirements of communication-intensive applications.

\begin{figure}[h]
	%\begin{center}
			\includegraphics[width=4.7in]{/home/madave/Dropbox/school/RP2/das4-routing/report/figures/fpx.jpg} 
	%\end{center}
	\caption{Degree-4 Photonic Cross-Connect. Image courtesy of TU Eindhoven and SURFnet}
\end{figure}
\vskip2em

Dynamic lightpath reservation, provisioning and release in the network is done by OpenNSI (TODO ref), a generic implementation of the Open Grid Forum (OGF) Network Service Interface protocol(NSI) (TODO ref). By coupling OpenNSA with the remote management facilities offered by the Finisar DWP50 WSS (TODO geil thesis ref), 
the DAS-4 network allows granular control over lightpath reconfiguration which can be carried out in a sealmess fashion by both researches and autonomous application code.

\section{Research Question \& Approach}

Transparent optical mesh networks facilitate dynamic end-to-end lightpath provisioning. Coupled with DWDM transport, such networks address constraints such as path and capacity allocation in an automated way. Achieved at Layer 0, dynamic lambda provisioning introduces additional considerations in terms of the existing IP overlay network that flows above it, namely dynamic topology reconfiguration. The bottom part of Fig x a. illustrates the two main considerations that arise. 
Lightpaths (links) connecting Layer 3 nodes may be allocated at will, which results in nodes changing their position in the topology and therefore their neighbors. Given nodes VU, ASTRON and UvA, where the dots of nodes are synonymous to the routers at each respective cluster, it can be seen that in one topology configuration nodes VU and UvA share a direct lightpath  whereas in another configuration they may be separated by the intermediate hop ASTRON. In addition, given nodes VU and ASTRON, a single lightpath may be assigned between the nodes with the purpose of providing connectivity at default line speeds, whereas in an alternate configuration multiple lightpaths may be assigned between them in order to achieve higher link speeds. In such a configuration, multiple optical interfaces at each node need to be paired which results in logical addressing, routing and link aggregation changes.

Each cluster of the DAS-4 network contains a router, or otherwise stated - a head node. Head nodes, represented by multi-purpose Linux platforms, are equipped with separate interfaces for connecting to the SURFnet StarPlane network (TODO ref), the Internet and the computational equipment part of the cluster. Four 10Gbps optical transceivers are used for connecting to StartPlane. Currently, the IP routing problem introduced by the dynamic lightpath allocation process is approached by using configuration scripts run manually on head nodes after each (dynamic) reconfiguration. The scripts handle interface IP addressing, the insertion of rules for static routing and capacity provisioning via Link Aggregation Control Protocol (LACP).  

Therefore the following research question can be defined: 

\begin{center}
\emph{What are the most suitable technologies for maintaining logical addressing and routing in DAS-4 dynamically reconfigurable network?}
\end{center}

Subsequently, the focus examines the following subquestions:

\begin{itemize}
    \item \emph{What is the applicability of Transport Layer protocols such as SCTP and MPTCP?}
    \item \emph{What is the applicability of routing protocols such as OSPF?}
    \item \emph{What is the applicability of link-bonding protocols such as LACP?}
\end{itemize}

different topologies may be constructed so that a higher capacity provisioning is achieved between the clusters. Higher capacity between two clusters is achieved by allocating multiple wavelengths. Equipped with multiple 10Gbps interfaces 


Such behavior causes nodes to either completely change their relative location with regards to a node considered as the point of origin in the topology by moving behind another one, or preserve their location with regards to a node but 






- abstract needs to point out that this is not primarily generic research but rather aims at expanding the current DAS-4 optical network based on its particular components(ROADMs, PXCs), systems(linux, SFPs) and capabilities(system scripts, etc)....
- reconfig opti nets still only studied in research testbeds. aim to be applied at a global level
- check if OpenNSA solved RWA and need for GMPLS or is this only for  o/e/o nets (GMPLS).
- the project is looking for a system that would aid the process of dynamic link and capacity provisioning preformed by OpenNSA, PXC and DWDM.


DAS-3 consists of
five clusters distributed over four sites and uses a dedi-
cated wide-area interconnect based on lightpaths, which
are provided by the fully optical DWDM backbone of
SURFnet-6 [25] (the Dutch NREN). Besides using 1 and
10 Gbit/s Ethernet, DAS-3 uses Myri-10G networking tech-
nology from Myricom [18] both as an internal high-speed
interconnect and as an interface to remote DAS-3 clusters.
The TUD cluster is only equipped with 1 Gbit/s Ethernet
locally. Every cluster uses dual-CPU AMD Opteron nodes,
but with different clock speeds and/or number of cores,
making DAS-3 somewhat heterogeneous.

The Distributed ASCI SuperComputer (DAS) is a collection of ve clusters
located in four Dutch Universities: the UvA and the VU in Amsterdam, the
University of Leiden and the Technical University in Delft. DAS is now in
its third implementation and is called DAS-3. The 270 dual-CPU nodes are
integrated into a single large-scale distributed system that provides a test-bed
for Grid applications and distributed systems.

The number of deployments of reconfigurable photonic cross-connects (PXCs) is increasing due to their ability to
economically enable flexaible topology evolution and handle rapid, yet unpredictable, bandwidth growth trends.
Supporting mesh network architectures, these networks allow the replacement of costly opto-electronic conversions
between previously optically isolated network domains with reconfigurable all-optical interconnections. Also,
network operatoraas can increase the efficiency and utilization of their networks by strategically increasing the mesh
connectivity between nodes



This list here i need to reiterate in the next chapter ?
- introduce DAS-4
- intro PXC
  - WSSs main charac of reconfigurability
  - In addition, the PXC provides dynamic labmda allocation + end-to-end
  - Each cluster contains a Linux router equipped with multiple 10Gbps 
- intro OpenNSI
  - rwa calculations 
  - end-to-end alloc
  






\vspace{3cm}

Use the following items in the following order:
\hspace{10em}
\begin{itemize}
    \item Introduce photonic cross connects
    \item Explain what they are and what they do
    \item Explain what is the network
    \item Explain what is the problem
\end{itemize}

\begin{itemize}
    \item Provide research questions
    \item Detect new insights
\end{itemize}






\section{Thesis outline}
